1. Field of the Invention
This invention relates to a method of making a magnetic recording medium such as a magnetic tape. This invention particularly relates to a method of making a magnetic recording medium, wherein press processing (hereinafter referred to as calendering) is carried out efficiently.
2. Description of the Prior Art
In general, magnetic recording media (hereinafter referred to as magnetic tapes) used for video tape recorders or the like are subjected to surface processing, which is called calendering, for the purpose of improving their electromagnetic transducing characteristics. Calendering is carried out by alternately disposing a plurality of metal rolls and resilient rolls or disposing only the metal rolls, moving a magnetic tape comprising a substrate and a recording layer formed of a ferromagnetic material and overlaid on the surface of the substrate between the rolls, and thus pressing the magnetic tape at a predetermined temperature under a predetermined pressure, thereby to smooth the surface of the magnetic tape and improving the packing density of the recording layer.
However, when the magnetic tape is subjected to calendering just after the ferromagnetic material is applied and dried, protrusions on the surface of the recording layer become separated as magnetic grains. Thus chipping occurs in the course of calendering. As a result, the surfaces of the calender rolls composed of the metal rolls and the resilient rolls are roughened by chipping, and the calendering effects are deteriorated. In addition, dents can occur on the surface of the recording layer and cause the recording layer to peel off from the magnetic tape thereby creating drop-out. Also, it takes a long time to repair surfaces of the calender rolls which have been roughed by chipping, i.e., to make such surfaces smooth again and therefore the productivity becomes low.